Defect states, doping related

Solitons are considered to be important defect states in these conjugated polymers (see Fig. 6.48). It has however been shown that correlation energy is the more important factor in giving rise to the energy gap in (CH) (Soos Ramasesha, 1983). Other polymers related to polyacetylene are polythiophene, polypyrrole, poly-phenylenesulphide, and polyparaphenylene (Section 3.3). Extensive measurements on doped polyacetylenes have been reported in the last five years and these materials, unlike other conducting polymers such as (SN), seem to have good technological potential. 

Traps and recombination centers which depend on purity, crystal defects and preparation, can exert an influence, and electrode contacts, carrier injections, and other factors can interfere with measurements. Yet there is no doubt that the photoconductive gain (quantum yield) G can be reproduced by different methods. As in the case of dark conductivity, the photoconductivity properties are related to the electronic and structural behavior of pure and doped organic compounds, also those in the polycrystalline state. 

A variety of related structures can be identified with 6,8, and 12-fold coordination of the A cation and four or sixfold coordination of the anion. In fact, the chemistry of ABO4 temarys is extremely complicated with solid solutions and phase transitions being common. Lattice defects may be introduced easily by appropriate dopings. Scheelites and its relatives have been studied intensively for their properties as heterogeneous catalysts, as host materials for impurity activated luminescent materials, and for specialized optical uses see Oxide Catalysts in Solid-state Chemistry and Section 4.4). 

Doping azides with selected impurities has received attention because it alters the decomposition kinetics. By relating the changes to the defect structure and the electronic states introduced by the impurities, probable reaction mechanisms can be inferred. 

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